This invention relates to improved hydrocarbon fuels which control the octane requirement increase (ORI) phenomenon observed during the initial portion of the operating life of spark ignition internal combustion engines.
The octane requirement increase (ORI) effect exhibited by internal combustion engines, e.g., spark ignition engines, is well known in the art. This effect may be described as the tendency for an initially new or clean engine to require higher octane quality fuel as operating time accumulates and is coincidental with the formation of deposits in the region of the combustion chamber of the engine. Thus, during the initial operation of a new or clean engine, a gradual increase in octane requirement (OR), the fuel octane number required for knock-free operation, is observed, accompanied by an increasing build-up of combustion chamber deposits until a rather stable or equilibrium OR level is reached. At the equilibrium OR level the accumulation of deposits on the combustion chamber surfaces no longer increases, but remains relatively constant. This so-called "equilibrium value" is usually reached between about 3,000 and 20,000 miles or the corresponding hours of operation. The actual equilibrium value of this increase can vary with engine design and even with individual engines of the same design; however, in almost all cases the increase appears to be significant. ORI values ranging from about 2 to 14 Research Octane Numbers (RON) are commonly observed in modern engines.
It is known that additives may prevent or reduce deposit formation, or remove or modify formed deposits, in the combustion chamber and adjacent surfaces and hence decrease OR. Such additives are generally known as octane requirement reduction (ORR) additives.
For example, in U.S. Pat. No. 4,264,335 to Bello et al., the cerous or ceric salt of 2-ethylhexanoate is disclosed as a useful additive for suppressing the octane requirement increase of a gasoline fired internal combustion engine. It is noted in this patent that the above salt has no effect on combustion efficiency of a gasoline and does not provide anti-knock properties.
In U.S. Pat. No. 4,357,148 to Graiff an additive is disclosed for controlling or reversing the octane requirement increase of a spark ignition internal combustion engine which comprises a combination of (a) certain oil-soluble aliphatic polyamines and (b) certain low molecular weight polymers and/or copolymers of monoolefins having up to 6 carbon atoms.
U.S. Pat. No. 3,506,416 to Patinkin et al. discloses an additive to inhibit octane requirement increase of a spark ignition engine which comprises a gasoline soluble metal salt of a hydroxamic acid. This additive is disclosed as useful in leaded gasolines. Nickel and cobalt are especially preferred as the additives. In U.S. Pat. No. 4,444,565 to Croudace, on the other hand, an oil-soluble iron compound in combination with a carboxylic acid or ester is added to the combustion intake charge of an internal combustion engine to suppress the octane requirement increase. And U.S. Pat. No. 4,217,111 to Frost, Jr., discloses a fuel composition containing gasoline and an octane requirement moderating additive comprising a dialkyl formamide of 7 to 11 carbon atoms.
Other references describing additives for inhibiting octane requirement increase include U.S. Pat. Nos. 3,144,311 and 3,146,203, which disclose utilization of nitrogen ring compounds in combination with an organo metallic primary anti-knock agent and a minor amount of an ignition control additive selected from the group consisting of phosphoric and boron compounds. And U.S. Pat. No. 3,817,721 discloses the use of high molecular weight alkyl aromatic hydrocarbons, or mixtures thereof, for reducing intake valve deposits formed in a spark ignition gasoline-fueled internal combustion engine.
In addition to the foregoing, another known additive for inhibiting ORI is polyaminopolyether carbamate, marketed commercially as Techron, by Chevron Oil Company, and described more fully in U.S. Pat. No. 4,270,930 to Campbell et al. Techron is the industry standard for ORI inhibition, but improvements beyond those afforded by Techron are still being sought. In particular, additives are needed which provide either more inhibition of ORI in engines and/or more reduction in engine OR from their "equilibrium values." More particularly still, an additive is needed which will provide such inhibition or reduction at relatively low concentrations in gasoline.